Light-producing display having high aperture ratio pixels

ABSTRACT

A method of making a tiled emissive display having at least two aligned tiles including finishing at least one edge of each tile and aligning the finished edges of such tiles and forming a monolithic structure including aligned tiles, each such aligned tile having a substrate, TFT circuits, drive circuits and bottom pixel electrodes for providing electrical signals to pixels in the corresponding tile. The method also includes coating the aligned tiles with material that produces light when activated by an electric field and forming at least one top pixel electrode over the coated material so that the coated material produces light when activated by an electric field from the electrode.

FIELD OF THE INVENTION

[0001] The present invention relates generally to tiled emissivedisplays, which include a plurality of tiles, which are aligned toproduce an image.

BACKGROUND OF THE INVENTION

[0002] Flat panel technology has been dominated by liquid crystaldisplays (LCD's) in which the liquid crystal material acts as a valve totransmit light from a back light source. Large displays are usuallysmaller displays tiled together. For large LCD panels the tile buildingblocks are generally complete displays with the liquid crystal materialin the cavity defined by two glass plates that are sealed around theperimeter. The edges of the sealed tiles are cut and polished tominimize the distance from the edge pixel to the edge of the tile. Theintegrity of the seal around the LCD material must be maintained therebylimiting the amount of cutting and polishing that is possible.Furthermore, variability in the performance from one tile to another cancreate discontinuities in the large panel image. The tiles are usuallytested and sorted to minimize tile variability.

[0003] U.S. Pat. No. 5,980,348 describes a method for aligning andattaching LCD tiles for large panel displays. A mechanical alignmentsystem is employed. U.S. Pat. No. 5,903,328 describes tiled LCD displayswhere the adjacent tile edges are ground at an angle and overlap eachother. This allows a small increase in the space for the ground edgerelative to the adjacent pixels; however, as the space increases thedistance between the image planes of adjacent tiles increasesproportionally. U.S. Pat. No. 5,889,568 describes a tiled LCD displaywherein masking techniques are used to hide the seams between tiles. Themask can be positioned behind of the LCD tile to block stray light fromthe back light as well as in front of the tile. U.S. Pat. No. 5,781,258describes an LCD tiled display wherein the half tiles are used and thefinal filling of the LCD material is completed within the cavity of allthe tiles simultaneously.

[0004] Emissive displays, which produce their own light, have a verydifferent structure from LCDs. The emissive material is deposited on tothe substrate surface. A back plate or thin film coating providesprotection from the environment. The organic and polymeric materialsthat produce light are sensitive to environment, heat and dirt. Thepreparation of the edges of emissive tiles is difficult due to thepotential exposure to contaminants.

SUMMARY OF THE INVENTION

[0005] It is an object of the present invention to provide a large flatpanel tiled emissive display with continuity of the pixels, both inlight-emitting characteristics and in spacing, across the display area.

[0006] This object is achieved by a method of making a tiled emissivedisplay having at least two aligned tiles, comprising the steps of:

[0007] a) finishing at least one edge of each tile and aligning thefinished edges of such tiles;

[0008] b) forming a monolithic structure including aligned tiles, eachsuch aligned tile having a substrate, TFT circuits, drive circuits andbottom pixel electrodes for providing electrical signals to pixels inthe corresponding tile;

[0009] c) coating the aligned tiles with material that produces lightwhen activated by an electric field; and

[0010] d) forming at least one top pixel electrode over the coatedmaterial so that the coated material produces light when activated by anelectric field from the electrode.

ADVANTAGES

[0011] It is an advantage of the present invention that individual tilescan be prepared, aligned and joined together prior to the deposition oflight emitting materials. The aligned tiles are processed as amonolithic structure. By coating the joined tiles as a single flatpanel, the process of polishing, squaring and aligning the edges of thetiles is complete prior to deposition. The preparation of the edges ofthe tiles produces many particles and is serious source ofcontamination; in the present invention, the debris from theseoperations can be removed prior to deposition of organic materials. Themonolithic structure can be cleaned and the light-emitting materials arethen deposited in a clean environment without further need to preparethe edges or handle the tiles for alignment.

[0012] It is a further advantage of the present invention that all thetiles in a single display are coated concurrently. Typically, for tilingof active matrix LCD displays, the tiles are sorted and characterizedand then tiled together. However, any variations are readily evident atthe seams. By coating all the tiles concurrently, the variations fromdifferent process runs and material lots are eliminated. Therefore, thetile-to-tile characteristics are indistinguishable across the seam.

[0013] It is a further advantage of the present invention that bycoating the tiles as a monolithic structure the coating can becontinuous across tiles thereby reducing coating edge effects within thetiled array. By eliminating the edge effects, active pixels can beplaced along the edge of the tiles to allow for pixel pitch integrityfrom tile to tile.

[0014] It is a further advantage of the present invention that thecoated monolithic structure can be immediately packaged and encapsulatedin its entirety. The monolithic structure is therefore more readilyprotected from the environment. Individual tiles do not need to behandled after deposition of the sensitive light emitting materials;elimination of this handling time greatly reduces risk of environmentaldegradation and increases yield and reliability of the display.

[0015] It is a further advantage of the present invention that highertemperature joining techniques can be used to bond tiles to make themonolithic structure. By bonding the tiles prior to deposition of thelight emitting materials high temperature processes including metalbonding, high temperature adhesive, microwave bonding, and fusionjoining can be used. In addition, ultraviolet light activated adhesivescan be used prior to deposition of light emitting material.

[0016] It is a further advantage of the present invention thatelectrical interconnections to the monolithic structure can beestablished prior to coating deposition. Connection techniques thatrequire high temperature, ultrasonics or pressure can be used only whenthe light emitting materials are not present. By positioning the tilesprior to deposition of the light emitting material, electricalconnections can be made to a back plate by means including soldering,ultrasonic bonding, microwave bonding, and conductive adhesives.Furthermore, electrical escapes including attachment of flex connectionsat high temperatures including soldering, can be established. Cleaningof the monolithic structure after electrical connections are made andprior to deposition of the light emitting materials facilitates highquality displays.

[0017] It is a further advantage of the present invention that it issuitable for use in organic electroluminescent displays. A feature ofthe invention is that it can be readily manufactured and the displaywill not produce artifacts caused by aligned tiles.

[0018] It is advantageous to prepare the tile edges and align the tilesprior to deposition of the light emitting materials.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a composite of a monolithic structure with drivecircuits on the edges outside the display area;

[0020]FIG. 2 is a cross section of the monolithic structure shown inFIG. 1. with bottom emitting pixels and color filters under the pixel;

[0021]FIG. 3 is a cross section of the monolithic structure shown inFIG. 1. with top emitting pixels and color filters coated on a topplate;

[0022]FIG. 4 is a cross section of the monolithic structure shown inFIG. 1. with pattern coated top emitting pixels of different color;

[0023]FIG. 5 is a cross section of the monolithic structure shown inFIG. 1. with pattern coated bottom-emitting pixels of different colors;

[0024]FIG. 6 is a composite of a monolithic structure including anisland tile with TFT circuits and driver circuits under the displaypixels;

[0025]FIG. 7 is a cross section of the monolithic structure shown inFIG. 6 with top emitting pixels and color filters coated on a top plate;

[0026]FIG. 8 is a cross section of the monolithic structure shown inFIG. 6 with pattern coated top emitting pixels of different colors;

[0027]FIG. 9 is a top view of a temporary coating support fixture;

[0028]FIG. 10 is a front view of the coating support fixture shown inFIG. 9;

[0029]FIG. 11 is a side view of the coating support fixture shown inFIG. 9;

[0030]FIG. 12 is a cross section of a simple emissive pixel structure;and

[0031]FIG. 13 is a cross section of a top emitting pixel structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Turning now to FIGS. 1-5, a composite view of a monolithicstructure 20 is shown for an emissive display. The monolithic structure20 is composed of tiles 22 a-d that are preprocessed for edge quality.The tiles 22 have thin film transistor (TFT) circuits 40 and bottompixel electrode 104 or 304 arrays defining the active area of thedisplay. The drive electronics 34 and TFT 40 circuits provide electricalsignals to pixels 100 in the corresponding tile. It is understood thatthe tiles 22 can be tested to ensure proper performance of the TFTcircuits 40 and drive circuits 34. The edges of the tiles 22 arepolished to maintain a parallel line to the bottom pixel electrode 104or 304 array. Furthermore, the polishing reduces the distance from theoutermost pixel to the tile 22 edge. The tiles 22 are aligned with aposition so that the pixel pitch 36 across the seam of the adjacenttiles is approximately equal to the pixel pitch 36 within the array of asingle tile. The tiles 22 can be affixed to each other using adhesive.Furthermore, higher temperature joining techniques can be used to bondtiles to make the monolithic structure 20. Light emitting materials aresensitive to temperature and ultraviolet light; this severely limits theoptions for bonding tiles together. By bonding the tiles prior todeposition of the light emitting materials 108 or 308 high temperatureprocesses including metal bonding, high temperature adhesive, microwavebonding, and fusion joining can be used. In addition, ultravioletadhesives can be used prior to deposition of light emitting material 108or 308. The proximity of the pixel area to the space 32 between tilesprecludes the ability to mask only the pixel area; therefore, it wouldnot be possible to use ultraviolet processes after deposition. Prior todeposition of the light emitting material 108 or 308 the monolithicstructure 20 can be thoroughly cleaned.

[0033] Light emitting material 108 or 308 is deposited onto themonolithic structure 20. It is understood that the light emittingmaterial 108 or 308 can be several materials that when layered orcombined provide the desired light emitting properties when activated byan electric field. In addition, it is understood that the monolithicstructure 20 can be supported by a carrier throughout processing. Thematerial can be deposited in numerous ways including, but not limitedto, evaporation, sublimation, and spin coating. The coatings 108 or 308can be continuous across the monolithic structure 20, extending beyondthe edge of the tiles 22 and covering the space 32 between tiles 22.When the coating is continuous the light emitting material 108 or 308 ismonochromatic, with the preferred embodiment being white light emitting.The coatings 108 or 308 include an electroluminescent material thatproduces light when activated by an electric field. The top pixelelectrode 106 or 306 is subsequently deposited over the light emittingmaterials in the coatings 108 or 308. The top pixel electrodes 106 or306 require a low work function conductive material.

[0034] When pixels 100 are bottom emitting as shown in FIG. 2 colorfilters 42 and a passivation layer 44 can be formed on the tiles 22prior to depositing the light transmissive bottom pixel electrode 104.The color filters 42 are aligned with bottom-emitting pixels 100 and canbe patterned to provide a full color display; one color combinationbeing red, green and blue.

[0035] In another embodiment where the multilayer organic top emittingpixels 300 are top emitting and have a light transmissive top pixelelectrode 306 a and b the color filters 42, which are aligned to themultilayer organic top emitting pixels 300, and the passivation layer 44can be formed on a top plate 46 that serves as the viewing plane for thedisplay. The color filters 42 can be patterned to provide a full colordisplay; one color combination being red, green and blue.

[0036] In another embodiment where pixels 100 are bottom emitting asshown in FIG. 5, the light emitting material 108 is pattern deposited onthe bottom pixel electrodes, 104 and viewed through the bottom. Thedeposition can be accomplished by evaporation, sublimation, or othermeans. Additionally, different pixels 100 can emit different coloredlight including patterned color combinations that produce a full-colordisplay. Alternatively, if the multilayer organic top emitting pixels300 are top emitting as shown in FIG. 4 the light emitting material 308is pattern deposited on the bottom pixel electrode 304 and viewedthrough the top pixel electrode 306.

[0037] In the preferred embodiment as shown in FIGS. 6-8, the monolithicstructure 20 can include island tiles 22 i. Island tiles 22 i are thosetiles that do not have any drive circuits 34 at the perimeter of themonolithic structure 20. All of the tiles 22 are mounted on a back plate30 to form a monolithic structure 20, which can then be coated. Theisland tiles 22 i can have vertical electrical connections to conductorson the back plate 30. Additionally, it is understood that the TFTcircuits 40 and the drive circuits 34 can be moved under the bottompixel electrodes 104 or 304 in order to allow pixels along all fouredges of the island tile 22 i as disclosed in commonly assigned U.S.patent application Ser. No. 09/788,923 filed Feb. 20, 2001, entitled“Light-Producing High Aperture Display Having Aligned Tiles” by Henry R.Freidhoff et al., the disclosure of which is incorporated herein byreference.

[0038] In a further embodiment the tiles 22 are properly aligned andthen affixed to back plate 30. The back plate 30 becomes a permanentpart of the monolithic structure 20 and provides support when operatedas a final display. The space 32 between the tiles can be, but need notbe, filled by adhesive or other means. Desiccant or an oxygen getteringmaterial can also be placed in the space 32. The tiles 22 are affixed tothe back plate 30 by adhesive, metal bonding, or other means.Furthermore, the back plate 30 can be used to escape signal lines fromthe tiles 22. Electrical connections can be made from the tiles 22 ofthe monolithic structure 20 to the back plate 30. These connections canbe made with conductive adhesive, flex, solder or other means. Theconnections can be made to vertical connections or run down the edges ofthe tile 22.

[0039] In another embodiment, a temporary support fixture 50, as shownin FIGS. 9-11, is used to temporarily secure tiles 22 for coating as amonolithic structure 20 wherein the temporary support fixture 50 is nota permanent support plate. In addition to providing support duringconcurrent tile 22 coating, the temporary support fixture 50 providesprotection of the polished edges of the tiles 22. The tiles 22 are laterremoved from the temporary support fixture 50 and realigned and mountedin the final assembly. The alignment and the spacing of the tiles 22 inthe temporary support fixture 50 are not critical during coating of thelight emitting layer 108 or 308 and top pixel electrode 106 or 306. Thecoatings 108 or 308 and 106 or 306 can extend beyond the edge of thetiles to provide uniform coverage across all tiles.

[0040] As shown in FIGS. 2, 3, 4, 5, 7 and 8 a polarization layer 48 canbe added to the viewing surface either the top plate 46 or back plate 30to increase the contrast ratio of the display.

[0041] The present invention is applicable to emissive displays, and isparticularly suitable for, but not limited to, use in organicelectroluminescent, EL, displays. FIGS. 12 and 13 show examples ofpixels 100 and 300 with organic EL materials.

[0042] A light-emitting layer of an organic EL tile comprises aluminescent or fluorescent material where electroluminescence isproduced as a result of electron-hole pair recombination in this region.In the simplest construction of a light-emitting pixel 100, as shown inFIG. 12, the light-emitting layer 108 is sandwiched between the bottompixel electrode or 104 and top pixel electrode 106. The light-emittinglayer is a pure material with a high luminescent efficiency. Awell-known material is tris (8-quinolinato) aluminum, (Alq), whichproduces excellent green electroluminescence.

[0043] The simple structure 100 can be modified to a three-layerstructure in which an additional EL layer is introduced between the holeand electron-transporting layers to function primarily as the site forhole-electron recombination and thus electroluminescence. In thisrespect, the functions of the individual organic layers are distinct andcan therefore be optimized independently. Thus, the electroluminescentor recombination layer can be chosen to have a desirable EL color aswell as high luminance efficiency. Likewise, the electron and holetransport layers can be optimized primarily for the carrier transportproperty.

[0044] In a preferred embodiment when the top plate 46 is the viewingsurface, the multilayer organic top emitting pixel 300, as shown in FIG.13, emits light from the top and has a substrate 302 on which isdisposed a light reflective conductive bottom pixel layer 304. Thebottom pixel electrode 304 comprises two layers 304 a and 304 b. 304 ais a light reflective conductive metal layer and 304 b is a thin lighttransmissive layer of a conductive high work function material. Anorganic light-emitting structure 308 is formed between a top pixelelectrode 306 and a bottom pixel electrode 304. The top pixel electrode306 is composed of two layers 306 a and 306 b. 306 a is a thin lighttransmissive conductive layer of a low work function material and 306 bis a light transmissive conductive layer such as indium tin oxide. Theorganic light-emitting structure 308 is comprised of, in sequence, anorganic hole-transporting layer 310, an organic light-emitting layer312, and an organic electron-transporting layer 314. When an electricalpotential difference (not shown) is applied between the bottom pixelelectrode 304 and the top pixel electrode 306, the top pixel electrode306 will inject electrons into the electron-transporting layer 314, andthe electrons will migrate across layer 314 to the light-emitting layer312. At the same time, holes will be injected from the bottom pixelelectrode 304 into the hole-transporting layer 310. The holes willmigrate across layer 310 and recombine with electrons at or near ajunction formed between the hole-transporting layer 310 and thelight-emitting layer 312. When a migrating electron drops from itsconduction band to a valence band in filling a hole, energy is releasedas light, and is emitted through the light-transmissive top pixelelectrode 306.

[0045] The invention has been described in detail with particularreference to certain preferred embodiments thereof, but it will beunderstood that variations and modifications can be effected with thespirit and scope of the invention. PARTS LIST  20 monolithic structure 22 tile  22a-d tiles with drive circuits at the edges beyond the pixels 22e-m tiles with circuits and drive circuits under the pixels  30 backplate  32 gap between adjacent tiles  34 drive circuit  36 pixel pitch 38 signal connection  40 TFT circuit  42 color filter  44 passivationlayer  46 top plate  48 polarization layer  50 temporary support fixture100 pixel 104 bottom pixel electrode 106 top pixel electrode 108light-emitting layer 300 multilayer organic top emitting pixel 302substrate 304 bottom pixel electrode 304a light reflective conductivemetal layer 304b high work function conductive material 306 top pixelelectrode 306a low work function conductive material 306b lighttransmissive conductive layer 308 organic light-emitting structure 310organic hole-transporting layer 312 organic light-emitting layer 314organic electron-transporting layer

What is claimed is:
 1. A method of making a tiled emissive displayhaving at least two aligned tiles, comprising the steps of: a) finishingat least one edge of each tile and aligning the finished edges of suchtiles; b) forming a monolithic structure including aligned tiles, eachsuch aligned tile having a substrate, TFT circuits, drive circuits andbottom pixel electrodes for providing electrical signals to pixels inthe corresponding tile; c) coating the aligned tiles with material thatproduces light when activated by an electric field; and d) forming atleast one top pixel electrode over the coated material so that thecoated material produces light when activated by an electric field fromthe electrode.
 2. A method of making a tiled emissive display having atleast two aligned tiles, comprising the steps of: a) finishing at leastone edge of each tile and aligning the finished edges of such tiles; b)forming a monolithic structure including aligned tiles, each suchaligned tile having a substrate, TFT circuits, drive circuits and bottompixel electrodes for providing electrical signals to pixels in thecorresponding tile and mounting the tiles on a back plate; c) coatingthe aligned tiles with material that produces light when activated by anelectric field; and d) forming at least one top pixel electrode over thecoated material so that the coated material produces light whenactivated by an electric field from the electrode.
 3. A method of makinga tiled emissive display having at least two aligned tiles, comprisingthe steps of: a) finishing at least one edge of each tile and aligningthe finished edges of the tiles; b) forming a monolithic structure ofthe aligned tiles wherein each tile has a substrate, TFT circuits, drivecircuits and bottom pixel electrodes for providing electrical signals topixels being mounted to a temporary support fixture; c) coating thealigned tiles with material that produces light when activated by anelectric field; d) coating at least one top pixel electrode over thecoated material that produces light when activated by an electric field;e) removing the coated tiles from the temporary support fixture; and f)aligning and attaching the tiles to a permanent support back plate. 4.The method of claim 1 wherein the pitch between columns of pixels on alltiles is substantially the same and the pitch between rows of pixels onall tiles is substantially the same and the spaces between rows andcolumns of pixels on adjacent tiles are substantially the same as thespaces within a tile.
 5. The method of claim 2 wherein the pitch betweencolumns of pixels on all tiles is substantially the same and the pitchbetween rows of pixels on all tiles is substantially the same and thespaces between rows and columns of pixels on adjacent tiles aresubstantially the same as the spaces within a tile.
 6. The method ofclaim 3 wherein the pitch between columns of pixels on all tiles issubstantially the same and the pitch between rows of pixels on all tilesis substantially the same and the spaces between rows and columns ofpixels on adjacent tiles are substantially the same as the spaces withina tile.
 7. The method of claim 1 wherein the light emitting material isa monochromatic continuous coating and color filters are disposed underthe pixels.
 8. The method of claim 2 wherein the light emitting materialis a monochromatic continuous coating and color filters are disposedunder the pixels.
 9. The method of claim 3 wherein the light emittingmaterial is a monochromatic continuous coating and color filters aredisposed under the pixels.
 10. The method of claim 1 wherein the lightemitting material is a monochromatic continuous coating and a top platepattern coated with color filters is aligned with the pixels andattached to the tiles.
 11. The method of claim 2 wherein the lightemitting material is a monochromatic continuous coating and a top platepattern coated with color filters is aligned with the pixels andattached to the tiles.
 12. The method of claim 3 wherein the lightemitting material is a monochromatic continuous coating and a top platepattern coated with color filters is aligned with the pixels andattached to the tiles.
 13. The method of claim 1 wherein the lightemitting material is coated as discrete color emitting pixels arrangedin a pattern to provide full color display.
 14. The method of claim 2wherein the light emitting material is deposited as discrete coloremitting pixels arranged in a pattern to provide full color display. 15.The method of claim 3 wherein the light emitting material is amonochromatic continuous coating and a top plate pattern coated withcolor filters is aligned with the pixels and attached to the tiles. 16.The method of claim 1 wherein a top plate and back plate are attached tothe display.
 17. The method of claim 2 wherein a top plate is attachedto the display.
 18. A tiled emissive display made in accordance with themethod of claim 1.